When producing packaged food products, especially those which are commercially sterilised or treated for extended shelf life, it is important that the packaging laminate or material does not contain any defects or splices which could jeopardize the quality of the packaged product. Defects can arise during the production of the packaging material, and it is important that packages containing defective packaging material are sorted out.
At the production of a packaging laminate, a roll, which e.g. is about 1.5 m wide and about 4000 m long, of cardboard material is fed into a laminator for laminating with plastic and commonly also aluminum. In the laminator, spotwise oxidation of the plastic can occur or small particles might unintentionally be laminated in the packaging material.
Defects which arises from spotwise oxidation or particles in the laminator are known as single spot defects. An image scanner or a laser scanner present in the laminator detects defects and marks their location on the packaging material, commonly by adding a piece of adhesive tape to the rim of the packaging material.
At a later stage in the production, the packaging material goes through a manual doctoring procedure, wherein the piece of tape is manually located, the defect is inspected and a decision is taken on whether it should be cut away and a splice be performed or if it is insignificant and no measures have to be taken. If a splice is made, the package which in the end contains this splice must be discarded.
Splicing is also performed in a slitting unit, wherein the packaging laminate is cut into rolls of a proper width and length for use in a filling machine, e.g. rolls that can be 30 cm wide and 800 m long. Obviously it is sometimes necessary to perform a splice to produce rolls that have the correct length.
Splicing also occurs in the packaging machine. It is performed by the operator when a roll of packaging laminate is near its end, and a new roll of packaging laminate is spliced to the one presently in the machine to obtain continuous production.
Later on, in the packaging machine, the web of packaging laminate is passed between two opposite rolls, and the presence of the splice is detected by the rolls as a change of thickness in the packaging laminate. To facilitate this, the web has to be flat to ensure contact between the web and the rolls. The detection also has to be performed upstream of any sterilisation treatment of the web, since the rolls are in contact with the web, and, thus, would compromise the sterility of the web. However, the rolls work fairly well for a thicker material. For a thin packaging laminate the difference in thickness is smaller and more difficult to detect in this manner.
The detected position of the splice is stored in the memory of the packaging machine control system, and when the packaging laminate has been transformed into individual packages, the package which is deemed to contain the splice is discarded together with the package before and the package after.
Since the splice detection is performed early in the packaging machine, i.e. prior to sterilisation and forming, the web of packaging laminate has a certain way to travel through the packaging machine before the discarding of the package containing the splice takes place. During this travel there is always a risk of a certain dislocation of the web which leads to some uncertainty as regards the exact position of the splice, i.e. in which package it is located.
Because of this, the measure is taken of throwing out three packages, instead of just the one which should contain the splice, even though this leads to unnecessary loss of product.
As is apparent from the above, there is a need for an improvement as regards the handling of defects and splices, both as regards better certainty when discarding packages to achieve less unnecessary loss of product, and as regards better certainty in the detection of the splices, especially when a thinner packaging laminate is used.